How to change restpose of armature while still preserving animation data?
was able to achieve the required result with Blender MoCap tools. I used the T-Pose BVH file and applied rotation scale and location to the TPOSE and set it as restpose.. then i imported gallop BVH file and using mocap tools i mapped the rotations to the first armature.. I was then able to retarget to my Custom RIgify rig with usual workflow.